1. Field
At least some of the various embodiments are directed to radio frequency identification (RFID) tags for use with metallic articles and/or bodies of living organisms.
2. Description of the Related Art
Radio frequency identification (RFID) tags are used in applications such as goods identification in wholesale and retail sales, access cards (e.g., building access, garage access), and badging and identification of employees. Certain RFID tags use a dipole antenna or a loop antenna as the mechanism to receive interrogating or reader signals, and respond to reader signals. However, while dipole and loop and antennas work well in free space applications, when placed close to metallic articles or water (e.g., a human or animal body), antenna performance is severely degraded, in some cases rendering the RFID tag inoperable.
Other antenna types, such as “patch antennas,” also suffer performance degradation when proximate to metallic objects or water. Patch antennas are made of a metallic radiative element (the patch), placed over a ground plane that is also metallic. The patch antenna radiates (or receives) in a direction substantially perpendicular to a plane defined by the metallic radiative element, with the radiation (or reception) pattern being present on the same side of the ground plane as the radiative element. However, when the radiative element becomes positioned between the ground plane and a metallic article or animal body, the patch antenna performance is severely degraded.
As a specific example, consider an employee badge suspended on the employee's chest or belt, and the badge having an RFID tag with a patch antenna. When the ground plane of the patch antenna is between the radiative element and the employee's body, the patch antenna works properly; however, when the badge is turned around, the radiative element is shielded between the ground plane and the employee's body and thus the RFID tag may not operate properly. If the employee badge comprises a dipole or loop antenna rather than the patch antenna, suspending the tag proximate to the employee's body detunes the antenna and/or severely affects the directivity of the antenna. In either case, operation of the RFID tag is severely degraded.